A light emitting diode (hereinafter referred to as “LED”) is capable of emitting light with reduced electric power consumption and at increased brightness and has a prolonged lifespan. Thus, attention is paid to the LED as a light source for illumination apparatus which can substitute an incandescent lamp or a fluorescent lamp. Since the light quantity of a single LED is smaller than the light quantity of a fluorescent lamp, a light emitting device provided with a plurality of LEDs is used in a typical illumination apparatus that employs LEDs as a light source.
As one example of the light emitting device of this kind, there is known a light emitting device in which a penetrating wiring portion extending through a substrate from the front surface of the substrate to the rear surface thereof is embedded in the substrate and flip-chip LEDs are electrically connected to the wiring portion provided on the rear surface of the substrate through the penetrating wiring portion (see, e.g., Japanese Patent Application Publication No. 2005-175292 (JP2005-175292A)). Also known is a light emitting device in which a through-hole extending from the front surface of a substrate to the rear surface thereof is formed in the substrate and a wiring layer is arranged in the through-hole (see, e.g., Japanese Patent Application Publication No. 2006-54209 (JP2006-54209A)).
However, the light emitting device disclosed in JP2005-175292A has a complex wiring structure because the penetrating wiring portion is embedded in the substrate. Therefore, the manufacturing cost is likely to increase. Since the LEDs are mounted to the substrate through bumps, the contact area between the LEDs and the substrate becomes smaller. This makes it difficult to efficiently dissipate heat from the LEDs through the substrate. In addition, the light emitting device disclosed in JP2005-175292A is based on a premise that a face-down type element is mounted as for the flip-chip. Therefore, the light emitting device is not suitable for use with a face-up type element.
In the light emitting device disclosed in JP2006-54209A, irregularities are formed on the LED-mounting surface due to the wiring layer and electrodes. This may possibly reduce the adherence of an encapsulating member or the like covering an element. In case where the LEDs are encapsulated by filling a transparent resin into a hollow transparent lens, the resin may flow out due to the existence of irregularities, which may possibly generate voids and consequently reduce the manufacturing efficiency. Since the wiring layer serves as both an LED-mounting surface and an electric wiring line, the contact area between the LEDs and the substrate becomes smaller. This may possibly reduce the heat dissipation of the LEDs.